question about water pumps

[seattle]

Hey Ron Thanks for the great site. I have a little question about water pumps and i would be most grateful if you would please answer it for me. How many GPH model of water pump do you need?

I also discovered that 1/2 inch pvc pipe fits snug inside the mouth of the bottle, can you for see any major problems with using 1/2 inch? that would make it half as much to build. Any comments are greatly appreciated .Thank you